Consolidated Statement of Stockholders' Equity (unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income	Treasury Stock
Balance at December 31, 2015 at Dec. 31, 2014					$ 555,767
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 50,044
Other comprehensive income	(6,770)				(6,770)
Balance, March 31, 2016 at Mar. 31, 2015					548,997
Balance at December 31, 2015 at Dec. 31, 2015	4,523,967	$ 1,497	$ 3,148,409	$ 4,856,674	118,549	$ (3,601,162)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock plan exercises	(3,778)	3	(3,781)
Stock plan compensation expense	6,514		6,514
Change in tax benefit from share-based payment arrangements	1,835		1,835
Dividends	(32,448)			(32,448)
Acquisition of common stock	(258,454)					(258,454)
Net income	220,318			220,318
Other comprehensive income	106,691				106,691
Balance, March 31, 2016 at Mar. 31, 2016	$ 4,564,645	$ 1,500	$ 3,152,977	$ 5,044,544	$ 225,240	$ (3,859,616)